SET amp w/Neg feedback?

I prefer less feedback. I've owned amps that had adjustable feedback and they always sounded more musical with zero feedback.

This assumes that you have a reasonable power match between your amp and your speakers. If you don't, then a little feedback may sound like it provides greater control, but it will come at the expense of transparency, harmonics and tone. I prefer to correct the amp and speaker mismatch before I compensate by adding feedback.

In systems where big punch and power are desired more than sublety, I've heard push pull amps that I liked using up to about 6db of feedback. Any more than about 6db of feedback in any amp dampens harmonics and transparency too much for me. An example of an amp using about that much feedback that is very musical is the Tom Evans Linear A. Still, when compared to an excellent zero feedback amp, one gives up some harmonics, decay and transparency.

In short, I don't think an SET amp with more than 5db feedback is a "good thing" and I believe less is better.

Rleff, the key to that is a flat impedance curve. The Avalon Eidelon does that well, as well as most magnetic planars, whose impedance curve has nothing to do with box resonance :)

There is another issue- the difference in performance between low impedance speakers and high impedance. Actually, the difference in impedance has little to do with the speakers and everything to do with the amps: **all amplifiers** regardless of the technology, will sound better driving higher impedances. IOW if sound quality is your goal, it will be better served by an 8 or 16 ohm speaker as opposed to 4 ohms, all other things being equal.

Another way to put this is if you had a speaker with 2 woofers, 2 midrange units and 2 tweeters, and all the drivers were 8 ohms, it would sound better wired as a 16 ohm load than it would wired as a 4 ohm load, regardless of the type of amplifier involved.

OTOH if sound **pressure** is your goal, and you have a transistor amplifier, a 4-ohm speaker might be preferred.

Where I termed it "big punch and power" I think Ralph is calling it "sound **pressure**" and I believe his term is more precise. If that is the goal, I'm skeptical that a marginal addition or subtraction of negative feedback will have significant sonic benefit or detriment.

I do believe that when using a properly matched speaker and tube amp combination, that marginal reductions in feedback yield significant sonic improvements. If your goal is to hear the harmonic tones of a violin, be able to pick out the timpani skin from within Solti's 9th symphony, hear how Neil Young's rythm guitarist scrapes the side of the pick along the length of a string or hear the unique tone of Hendrix's marshall amp at any volume, then less feedback is better. Jeff

Ralph - Thank you. I greatly appreciate all of your contributions to this forum.

The equipment matching conversation that is all over high end audio is a direct result of the conflict of these two paradigms.

If there was one fact I wish I had known when I started my audio journey it would be this one.

Gentlemen,
Thanks for all of the great responses. Everyone basically confirmed my own thoughts about NFB. I have a Cary sli-80 all triode w/ zero NFB. Its so much better than the regular sli-80 and they only have about 5db nfb. There is just a huge dif in musicality with mine vs the regular sli-80's. I have been looking at getting a SET amp and I found out the other day that one of them that I was considering has 15db of nfb!!
I think it's good advice to stay with zero nfb amps. I have coincident speakers, so they work great with tubes.
Ralph I want to come to RMAF and hear one of your amps, looking forward to it.
Thanks
Mike